Acids, Bases, and Salts - SS1 Chemistry Past Questions and Answers - page 3

pH is a measure of the acidity or alkalinity of a solution. It quantifies the concentration of hydrogen ions (H+) present in a solution. The pH scale is a logarithmic scale that ranges from 0 to 14, where a pH of 7 is considered neutral, values below 7 indicate acidity, and values above 7 indicate alkalinity.

 

The significance of the pH scale lies in its ability to provide a standardised measure of acidity or alkalinity. It allows for easy comparison of the relative acidity or alkalinity of different solutions. The pH scale is widely used in various fields, including:

1. Chemistry and Chemical Analysis: pH is crucial in chemical reactions, as it affects reaction rates, solubility, and the behaviour of chemical species. It is used in analytical techniques to determine the pH of solutions and to control reaction conditions.

 

1. Environmental Science: pH plays a critical role in understanding and monitoring the health of aquatic ecosystems. The pH of water bodies impacts the survival of aquatic organisms and influences chemical reactions in water.

 

1. Medicine and Biology: pH is important in biological systems, as it affects enzyme activity, cell function, and the overall balance of bodily fluids. pH measurements are used in clinical diagnostics, such as blood pH monitoring, and in research related to cellular and molecular biology.

 

1. Agriculture: The pH of soil is a key factor in plant growth and nutrient availability. It determines the solubility and accessibility of essential nutrients for plants.

 

1. Food and Beverage Industry: pH is a crucial parameter in food production and quality control. It affects flavour, texture, and microbial stability. pH measurements are used in food processing, preservation, and product development.

Indicators are substances that undergo colour changes in the presence of different pH values. They are used to visually determine the approximate pH of a solution.

 

Indicators work by undergoing a chemical reaction that involves a change in the arrangement of their chemical structure, resulting in a change in colour. Different indicators have specific pH ranges over which they exhibit colour changes. Some common pH indicators include:

 

1. Phenolphthalein: This indicator is colourless in acidic solutions (pH < 7) and turns pink in alkaline solutions (pH > 8).

 

1. Methyl orange: It is red in acidic solutions (pH < 3.1) and yellow in alkaline solutions (pH > 4.4).

 

1. Bromothymol blue: This indicator is yellow in acidic solutions (pH < 6), green at neutral pH (around pH 7), and blue in alkaline solutions (pH > 7.6).

 

1. Litmus: Litmus paper turns red in acidic solutions (pH < 7) and blue in alkaline solutions (pH > 7).

 

Indicators are used as visual aids to estimate the pH of a solution, but they provide a qualitative rather than a precise measurement. They are particularly useful in educational settings, quick pH tests, and qualitative observations. In more accurate pH determinations, pH metres or digital indicators are preferred.